1. Field of the Invention
The present invention relates to a display device for displaying a color by using a plurality of primary or key colors including red (R), green (G), and blue (B) in combination, and particularly relates to an image-signal driving circuit for supplying image data to a display of the display device.
2. Description of the Related Art
Display devices capable of color display by using a liquid-crystal display, a light source, and a color filter in combination are known.
FIG. 12 shows the arrangement of the color filters provided in subpixels or dots 104 on a display 101 of a conventional display device. The subpixels 104, which are also sometimes described as subpixels, each comprise one color filter. The display 101 typically displays colors in display units called pixels. A pixel typically consists of red, blue, and green subpixels, side by side, which together combine to form a color for the pixel of the display. The subpixels take their color from the color of the filter for the subpixel of the display. Hence, a pixel forming colors from red, blue, and green subpixels will typically be part of a display configured with red (R), green (G), and blue (B) filters in the respective subpixel locations making up the display pixel.
In a horizontal direction of one form of display(i.e., along scan lines G1, G2, G3, and so on), the three kinds of color filters are disposed in an alternating order along the row, as for example R, G, B, R, G, B, and so forth. In a vertical direction (i.e., along signal lines S1, S2, S3, and so on), each column has a single kind of color filter. For example, an entire column of R-color filters are provided in subpixels between the signal lines S1 and S2. Hereinafter, the above-described arrangement of the color filters will be referred to as the vertical stripe configuration.
Hereinafter, the display unit for displaying one of the primary colors is referred to as a subpixel 104. Further, the display unit for displaying a color by using three primary colors including R, G, and B in combination, that is, three subpixels 104 with three kinds of color filters (such as disposed along the scan line for the vertical stripe configuration), is referred to as a pixel 108.
In a vertical stripe configuration, when the number of pixels disposed in a horizontal direction (i.e., along the scan lines) is n, the number of subpixels is three times the number of pixels, that is, 3n. VGA systems, for example, specify a display of 640×480 pixels. Since the number of pixels in the horizontal direction is n=640, the number of subpixels is 3n=3×640=1920. Accordingly, the number of signal lines is 3n=1920. The number of pixels in the vertical direction (i.e., along the signal lines) in VGA systems (using the vertical stripe configuration) is the same as the number of the subpixels, that is, 480. Consequently, the number of scan lines is 480.
FIG. 13 is a block diagram showing the configuration of a source driver Sd100 of the conventional display device. Typically, a subpixel in a display is addressed by applying voltage to a gate line that switches on the subpixel and allows a voltage charge from the source driver to be applied (i.e., along the signal lines from the source driver) to the subpixel. Source driver Sd100 comprises a shift register 9; a sampling register 10; a line latch 11, a level shifter 113, a D/A converter 114, and an amplifier 115. The source driver Sd receives image data DA, DB, and DC, which are three sequences of digital data, and outputs analog data to signal lines (source wiring) S1, S2, S3, and so forth on the display 101. That is, image data R, G, and B for each pixel are received respectively as image data DA, DB, and DC.
The source driver receives the image data for each subpixel in a digital format. For example, the image data DA, DB, and DC may correspond respectively to the intensities of the red, green, and blue subpixels. As a further example, if DA is an 8-bit signal corresponding to the red subpixel, 256 different red color intensities may potentially be represented by this digital signal.
As noted above, for each full color pixel, three distinct subpixels are employed. With a combination of red, green, and blue subpixels of various intensities, for example, a pixel may be made to appear to the human eye to be any of a variety of different colors. Thus, the number of colors that can be made by mixing red, green, and blue subpixels depends on the distinct grayscale intensities that can be achieved by the pixels in the display. The image data DA, DB, and DC are typically received by the source driver of the display device in parallel but are sent serially several bits at a time.
The source driver Sd controls operation of its shift register 9 to store image data for one line in the sampling register 10. The shift register 9 starts operating in response to a start pulse received concurrently with a clock signal, and outputs “1” (i.e., an active signal) sequentially to each stage of the sampling register 10. Next, each stage of the sampling register 10 stores the image data DA, DB, and DC in response to the active signal received at each stage.
The line latch 11 latches (stores) image data for one line at a time in accordance with a load signal after the sampling register 10 has stored the image data for one line.
The level shifter 113 receives 3n image data output from the line latch 11 and outputs the image data after converting the logic level thereof. The D/A converter 114 converts the image data that is a digital signal to an analog signal. At this time, the D/A converter 114 receives a gradation voltage and performs the conversion on the basis of the received gradation voltage. The amplifier 115 amplifies the analog signal (mainly for amplifying the voltage), transmits the amplified analog signal to the signal line, and drives the display 101.
FIG. 14 is a block diagram showing the configuration of the sampling register 10. The sampling register 10 comprises a buffer 16 and stages 10-1, 10-2, 10-3, 10-4, and so forth. The image data DA, DB, and DC received by the sampling register 10 is transmitted to each of the stages 10-1, 10-2, 10-3, 10-4, and so forth via the buffer 16. When the shift register 9 transmits a “1” to one of the stages 10-1, 10-2, 10-3, 10-4, and so forth, the stage stores the image data DA, DB, and DC received from the buffer 16, and transmits the stored image data DA, DB, and DC to the line latch 11.
The horizontal stripe configuration is an alternative display configuration and aligns three different kinds of color subpixels vertically by using known source drivers. Since pixels are addressed or activated on a display one line at a time, in order to drive a display using a horizontal stripe configuration, the order of inputting image data to the source driver must be different for horizontal stripe configurations as compared to the vertical stripe configurations. Thus, in order to convert the order of the image data (e.g. Da, DB, and DC) received by the conventional source and gate drivers in the conventional display device to an acceptable sequence for driving a display using a horizontal stripe configuration, the size of an external circuit for supplying image data to the source driver becomes large. Further, this external circuit cannot be used for displays having a vertical stripe configuration.